A low-dimensional coal-based hard carbon material with both high sodium storage capacity and high initial coulombic efficiency and its preparation method.

Abstract

This invention discloses a low-dimensional coal-based hard carbon material with both high sodium storage capacity and high initial coulombic efficiency (ICE), belonging to the technical field of alkali metal ion battery anode materials. The method involves liquid-phase oxidation and depolymerization of Xinjiang bituminous coal to obtain coal oxide nanosheets and coal oxide-based graphene quantum dots; crosslinking, self-assembly, and deoxygenation reduction of a mixture of coal oxide nanosheets and coal oxide-based graphene quantum dots, or coal oxide nanosheets, using amine-containing compounds to obtain a low-dimensional coal-based precursor; and then, during high-temperature calcination, using graphite plates to assist in the pyrolysis of the low-dimensional coal-based precursor to prepare a series of low-dimensional coal-based hard carbon materials. This low-dimensional coal-based hard carbon material, as an anode for sodium-ion batteries, exhibits both high sodium storage capacity and high initial coulombic efficiency (ICE), achieving a high efficiency of 0.02 A g. ‑1 The specific capacitance at the current density can reach up to 420.40 mA hg. ‑1 It also boasts a high ICE ratio of 91.97%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alkali metal ion battery negative electrode materials, and particularly relates to a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency and a preparation method thereof. BACKGROUND

[0002] At present, most of the energy storage systems with high energy density and long cycle life adopt lithium ion battery technology. However, with the consumption of lithium resources and the gradual rise of costs, it is essential to develop new types of electrochemical energy storage devices. Sodium ion batteries are attracting attention as a viable alternative to lithium ion batteries because of the abundance of sodium resources and the chemical composition compatible with mature lithium ion battery technology. However, the sodium ion storage capacity of the graphite-like negative electrode material that promotes the commercialization of lithium ion batteries is poor, which poses a great challenge to its application in sodium ion batteries. In 2000, Stevens and Dahn found that hard carbon has a reversible capacity of 300 mAh g -1 The existing precursors for producing hard carbon include biomass, resin, high molecular polymer, etc.; these precursors usually have high cost and low carbon yield, greatly increasing the overall manufacturing cost of sodium ion batteries. Therefore, it is essential to develop low-cost and high-performance hard carbon negative electrode materials for sodium ion batteries.

[0003] Coal is a high-quality, inexpensive and readily available fuel and an important chemical raw material, and is widely used in the fields of energy, chemical industry and materials. In terms of chemical composition, coal has a very high carbon content and is a natural precursor of carbon materials. In terms of molecular structure, coal has the characteristics of a macromolecular polymer, which can be considered as a rigid network structure formed by connecting multiple similar basic structural units in three-dimensional space through bridge bonds, with a high degree of cross-linking and the basic structural units being difficult to form parallel arrangements. In addition, there are a large number of oxygen-containing functional groups and side chain structures in coal, and the oxygen-containing functional groups will prevent the ordered rearrangement of graphite-like crystalline structures during pyrolysis and carbonization. After the dehydrogenation, condensation, hydrogen transfer and isomerization processes of coal at high temperatures, a coal-based hard carbon material with highly twisted structures of curved graphitized carbon layers stacked on each other and amorphous carbon connections, abundant nanopores and large interlayer spacing is formed. In recent years, researchers have carried out a large number of studies on the microstructure regulation and electrochemical sodium storage mechanism of coal-based hard carbon materials, and have confirmed that the graphite crystalline structure and defect sites are the key factors determining the sodium storage performance.

[0004] Currently, researchers mainly regulate the microstructure of coal-based hard carbon materials through high-temperature carbonization (X. Ou, D. Gong, C. Han, Z. Liu, Y. Tang, Adv. Mater., 2021, 11, 2102498), precursor pre-oxidation (H. Chen, N. Sun, Q. Zhu, et al., Adv. Sci., 2022, 9, 2200023) and heteroatom doping (J. Wan, S. Fan, J. Qu, et al., ACS Energy Lett., 2024, 9, 627-635.) strategies. However, the above methods have several problems: (1) increasing pyrolysis temperature can increase the short-range order of pseudo-graphitic domains, but also causes the decrease of interlayer spacing, which seriously reduces the reversible capacity and diffusion kinetics of metal ions; (2) changing the pre-oxidation degree of the precursor can regulate the graphite crystallite structure of coal-based hard carbon, but it is difficult to reverse the disorder of pseudo-graphitic domains; (3) heteroatom doping defects can change the electronic distribution of carbon skeleton and improve chemical inertness, but the strong binding energy of sodium ions and the occurrence of side reactions make the initial coulombic efficiency (ICE) of coal-based hard carbon anode materials lower. In recent years, the graphite crystal template induction method is considered to induce the partial lattice reconstruction of biomass-based hard carbon and promote the formation of graphite-like crystals, thereby improving the sodium storage capacity and ICE of coal-based hard carbon as a negative electrode of sodium ion batteries (X. Li, J. Sun, W. Zhao, et al., Adv. Funt. Mater., 2022, 32, 2106980). Unlike biomass precursors, the rigid cross-linked network structure of coal limits the "top-down" flexible regulation of the microstructure of coal-based hard carbon by the graphite crystal template induction method, which in turn makes it difficult to balance the reversible sodium storage capacity and ICE of coal-based hard carbon materials as a negative electrode of sodium ion batteries. SUMMARY

[0005] The present application provides a preparation method of a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency, in order to solve the problem of contradictory and competitive relationship between the graphite microcrystalline structure and defect sites of the existing coal-based hard carbon material. The Xinjiang bituminous coal is oxidized and depolymerized by a liquid phase oxidation method to obtain active components such as oxidized coal nanosheets (OC) and oxidized coal-based graphene quantum dots (GQDs). Secondly, the active components are cross-linked, self-assembled and deoxidized by an amine-containing compound to prepare a low-dimensional coal-based precursor with a simple molecular structure and easy adjustment from bottom to top. Finally, the coal-based precursor is calcined with the assistance of a graphite crystal template to control the carbon atom migration, atomic fragment rearrangement and lattice reconstruction during coal pyrolysis, and then the crystal quality is improved by high-temperature calcination, thereby preparing a low-dimensional coal-based hard carbon negative material with high sodium storage capacity and high ICE. Another technical problem to be solved by the present application is to provide a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency. The specific capacity of the low-dimensional coal-based hard carbon material as a negative electrode of a sodium ion battery can reach 420.40 mA h g -1 at a current density of 0.02 Ag -1 , and simultaneously has a high ICE of 91.97%.

[0006] Technical scheme: In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency, wherein Xinjiang bituminous coal is oxidized and depolymerized by a liquid phase oxidation method to obtain oxidized coal nanosheets and oxidized coal-based graphene quantum dots; a mixture of the oxidized coal nanosheets and the oxidized coal-based graphene quantum dots or the oxidized coal nanosheets is cross-linked, self-assembled and deoxidized by an amine-containing compound to obtain a low-dimensional coal-based precursor; and the coal-based precursor is calcined with the assistance of a graphite plate, and then high-temperature calcination is performed to prepare a low-dimensional coal-based hard carbon material with high sodium storage capacity and high ICE.

[0008] The preparation method of the low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency adopts a nitric acid / sulfuric acid oxidation system to oxidize and depolymerize Xinjiang bituminous coal for 3-6 h, and the mass / volume ratio of the coal powder to the oxidation system is 1 g:24 mL; the volume ratio of sulfuric acid to nitric acid is 1:1-3:1; preferably, the Xinjiang bituminous coal is oxidized and depolymerized by the nitric acid / sulfuric acid oxidation system for 5 h, and the volume ratio of sulfuric acid to nitric acid is 3:1.

[0009] The preparation method of the low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency, wherein the amine-containing compound is any one of ethylenediamine, octylenediamine, o / m / p-phenylenediamine, diethylenetriamine, triethylenetetramine, polyether amine, polyimide, piperazine or urea.

[0010] The preparation method of the low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency comprises the following steps:

[0011] The preparation method of the low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, wherein the graphite plate is any one of ordinary graphite, high-purity graphite, ultrahigh-purity graphite or highly oriented pyrolytic graphite, and the fixed pressure ranges from 3 to 30 kPa; preferably, the fixed pressure ranges from 3 to 20 kPa; further preferably, the fixed pressure is 20 kPa.

[0012] The preparation method of the low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, wherein the high-temperature calcination is heating to 800-1500°C under nitrogen atmosphere protection, the holding time is 1-6 h, and the heating rate is 1-10°C / min -1 ; preferably, the high-temperature calcination temperature is 800-1300°C, the holding time is 2-6 h, and the heating rate is 5-10°C / min -1 ; further preferably, the high-temperature calcination is heating to 1300°C, the holding time is 2 h, and the heating rate is 5°C / min -1 .

[0013] The preparation method of the low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency comprises the following steps:

[0014] (1) liquid-phase oxidation of Xinjiang bituminous coal in a nitric acid / sulfuric acid oxidation system, and obtaining oxidized coal nanosheets and oxidized coal-based graphene quantum dots through centrifugation, dialysis, rotary evaporation and cold drying;

[0015] (2) dissolving the mixture of oxidized coal-based graphene quantum dots and oxidized coal nanosheets or the oxidized coal nanosheets in deionized water, wherein the mass-volume ratio of the oxidized coal nanosheets to the deionized water is 1 g:100 mL;

[0016] (3) adding an amine-containing compound after the two are completely dissolved in water, and magnetically stirring for 1-8 h;

[0017] (4) Put the mixed solution into a hydrothermal kettle for hydrothermal reaction, so that the amine-containing compound is fully crosslinked with the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot;

[0018] (5) The crosslinked mixed solution is cold-dried to obtain a low-dimensional coal-based hard carbon precursor, which is sandwiched between two graphite plates, and a fixed pressure is applied to the graphite plates;

[0019] (6) The graphite plate sandwiching the low-dimensional coal-based hard carbon precursor is loaded into a tube furnace for high-temperature calcination in an inert atmosphere, and then cooled to obtain a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency.

[0020] The preparation method of the low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency, characterized by the preparation of the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot:

[0021] (a) Ball milling the Xinjiang bituminous coal raw coal to pass through a 200-mesh sieve to obtain coal powder;

[0022] (b) 30g of coal powder is added to a 5L measuring cylinder, and 720mL of a mixed solution of sulfuric acid and nitric acid is slowly added under stirring, the volume ratio of sulfuric acid to nitric acid being 1:1 to 3:1, and the reaction being carried out for 3-6h;

[0023] (c) After the reaction is completed, the mixture is diluted into 3L of deionized water, and centrifuged at a speed of 8000-10000rpm for 5-10min;

[0024] (d) After the upper layer of acid solution is poured out, the precipitate in the centrifuge tube is dissolved in 3-5L of deionized water, and after ultrasonic treatment for 1-3h to completely dissolve it, it is loaded into a dialysis bag for dialysis;

[0025] (e) After the solution is dialyzed to neutral, centrifugation is performed again, and the large particles that are not completely oxidized are precipitated, and the upper clear liquid is concentrated using a rotary evaporator at 60-80℃;

[0026] (f) Finally, the concentrated solution is freeze-dried to obtain the oxidized coal-based graphene quantum dot; and the large particle precipitate collected is the oxidized coal nanosheet.

[0027] The low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulomb efficiency prepared by the above method.

[0028] Advantages: Compared with the prior art, the present application has the following advantages:

[0029] (1) The present application extracts and transforms the aromatic basic structural units in coal into active components such as oxidized coal nanosheets and oxidized coal-based graphene quantum dots by liquid phase oxidation of Xinjiang bituminous coal.

[0030] (2) Using amine-containing small molecules as cross-linking agents, the active components are self-assembled by covalent bonding to construct low-dimensional coal-based precursor materials.

[0031] (3) By graphite crystal template-assisted calcination, the orderliness of pseudo-graphitic domains and the reduction of defect sites in the microstructure of coal-based hard carbon are increased, thereby preparing low-dimensional coal-based hard carbon sodium storage materials with high capacity and high initial coulombic efficiency.

[0032] (4) As a negative electrode for sodium-ion batteries, the specific capacity of the low-dimensional coal-based hard carbon material for sodium storage can reach 279.60-420.40 mA h g -1 at a current density of 0.02 A g -1 , while having a high initial coulombic efficiency of 85.53-97.59%.

[0033] (5) The low-dimensional coal-based hard carbon material has low preparation cost, simple process and excellent electrochemical performance, which can provide a technical basis for the commercial preparation of coal-based hard carbon negative electrode materials for sodium-ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 (a), (b), (c) are appearance photos of the low-dimensional coal-based precursor, the low-dimensional coal-based hard carbon, and the charge-discharge curve of the low-dimensional coal-based hard carbon material at a current density of 0.02 A g -1 , respectively, prepared in Example 1;

[0035] Figure 2 (a), (b), (c) are appearance photos of the low-dimensional coal-based precursor, the low-dimensional coal-based hard carbon, and the charge-discharge curve of the low-dimensional coal-based hard carbon material at a current density of 0.02 A g -1 , respectively, prepared in Example 2;

[0036] Figure 3 (a), (b), (c) are appearance photos of the low-dimensional coal-based precursor, the low-dimensional coal-based hard carbon, and the charge-discharge curve of the low-dimensional coal-based hard carbon material at a current density of 0.02 A g -1 , respectively, prepared in Example 3;

[0037] Figure 4 (a), (b), (c) are appearance photos of the low-dimensional coal-based precursor, the low-dimensional coal-based hard carbon, and the charge-discharge curve of the low-dimensional coal-based hard carbon material at a current density of 0.02 A g -1 , respectively, prepared in Example 4;

[0038] Figure 5 (a), (b), (c) are appearance photos of the low-dimensional coal-based precursor, the low-dimensional coal-based hard carbon, and the charge-discharge curve of the low-dimensional coal-based hard carbon material at a current density of 0.02 A g-1 Charge-discharge curves at different current densities;

[0039] Figure 6 (a), (b), (c) are appearance pictures of the low-dimensional coal-based precursor, appearance pictures of the low-dimensional coal-based hard carbon and appearance pictures of the low-dimensional coal-based hard carbon material at 0.02 Ag -1 Charge-discharge curves at different current densities;

[0040] Figure 7 (a), (b), (c) are appearance pictures of the low-dimensional coal-based precursor, appearance pictures of the low-dimensional coal-based hard carbon and appearance pictures of the low-dimensional coal-based hard carbon material at 0.02 Ag -1 Charge-discharge curves at different current densities. DETAILED DESCRIPTION

[0041] The application will be further illustrated below in combination with specific examples. The examples are implemented on the premise of the technical scheme of the application and should be understood as being used for illustrating the application rather than limiting the scope of the application.

[0042] Preparation of oxidized coal nanosheets and oxidized coal-based graphene quantum dots, comprising the following steps:

[0043] (a) The Xinjiang bituminous coal raw coal is ball milled and sieved through a 200 mesh sieve to obtain coal powder;

[0044] (b) 30 g of coal powder is added to a 5 L graduated cylinder, and 720 mL of a mixed solution of sulfuric acid and nitric acid (volume ratio of sulfuric acid to nitric acid is 3:1, reaction time is 5 h) is slowly added under a blender;

[0045] (c) After the reaction is completed, the mixture is diluted into 3 L of deionized water, and centrifuged at a speed of 9000 rpm for 8 min;

[0046] (d) After the supernatant acid is poured off, the precipitate in the centrifuge tube is dissolved in 5 L of deionized water, and after ultrasonic treatment for 3 h to completely dissolve it, it is loaded into a dialysis bag for dialysis;

[0047] (e) After the solution is dialyzed to neutral, centrifugation is performed again, and the large particles that are not completely oxidized are precipitated, and the supernatant is concentrated at 75°C using a rotary evaporator;

[0048] (f) Finally, the concentrated solution is freeze-dried to obtain oxidized coal-based graphene quantum dots; the large particles precipitated are collected to obtain oxidized coal nanosheets.

[0049] The oxidized coal nanosheets and oxidized coal-based graphene quantum dots prepared above are used in the following examples 1-7 for the preparation of low-dimensional coal-based hard carbon materials with high sodium storage capacity and high initial coulombic efficiency.

[0050] Example 1

[0051] A method for synthesizing a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, the precursor of the material being prepared by cross-linking and deoxidizing reduction of oxidized coal nanosheets and urea; specifically comprising the following steps:

[0052] Dissolve 0.30 g of oxidized coal nanosheets in 30 mL of deionized water, after complete dissolution, add 100 μL of urea solution to the magnetic stirrer and stir for 1 h, then pour the uniformly mixed solution into a 50 mL hydrothermal kettle, and incubate at 100℃ for 8 h to allow the oxidized coal nanosheets to fully cross-link with the urea; finally, the cross-linked liquid is cold-dried to obtain the precursor;

[0053] Put the cold-dried precursor between two ordinary graphite plates, and use an electric isostatic press to apply a pressure of 3 kPa to the graphite plates to ensure uniform contact of the precursor with the graphite plates. Then, put the graphite plates into a porcelain boat and place them in a tube furnace, pre-blow nitrogen for 0.5 h at room temperature to remove air in the tube; under nitrogen atmosphere, heat at a rate of 5℃ / min to 1000℃, and incubate for 3 hours. After cooling to room temperature, the sample is taken out, which is a low-dimensional coal-based hard carbon material. -1

[0054] The low-dimensional coal-based hard carbon material prepared above is used as the negative electrode of a sodium ion battery, and the sodium ion battery is assembled.

[0055] Mix the prepared sodium ion battery negative material powder, Ketjen black, and sodium carboxymethyl cellulose according to a mass ratio of 8:1:1, grind them thoroughly into fine powder, add an appropriate amount of deionized water to continue grinding into slurry with appropriate viscosity, uniformly coat the slurry on copper foil with a coater, and dry at 110℃ under vacuum for 10 h. Cut it into a circular negative electrode sheet with a diameter of 10 mm with a cutting machine for standby. In an argon-filled glove box, assemble a half-cell with metallic sodium as the counter electrode and 1 mol of NaPF6 dissolved in dimethyl carbonate as the electrolyte. Assemble a CR2025 type button cell, and after standing for 6 h, perform electrochemical charge and discharge tests. The test voltage range is 0.01V-3V, and the current density is 0.02Ag -1 The test results are shown in Figure 1 , the reversible specific capacity is 279.60mAh g -1 , the initial coulombic efficiency is 85.53%, and the material has good electrochemical sodium storage performance.

[0056] Example 2

[0057] A method for synthesizing a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, the material being prepared by cross-linking and deoxidizing reduction of oxidized coal nanosheets and oxidized coal-based graphene quantum dots with triethylenetetramine; specifically comprising the following steps:​

[0058] The oxidized coal nanosheet and the oxidized coal-based graphene quantum dot (0.30 g of the oxidized coal nanosheet, a mass ratio of the oxidized coal nanosheet to the oxidized coal-based graphene quantum dot being 5:1) were dissolved in 30 mL of deionized water, 200 μL of triethylenetetramine solution was added after complete dissolution, and the mixture was stirred in a magnetic stirrer for 2 h, then the uniformly mixed solution was poured into a 50 mL hydrothermal kettle, and the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot were allowed to be fully crosslinked with the triethylenetetramine solution under the condition of 110 ℃ for 6 h, and finally the crosslinked liquid was cold-dried to obtain a precursor;

[0059] The cold-dried precursor was clamped between two high-purity graphite plates, a graphite plate was subjected to a pressure of 6 kPa by using an electric isostatic pressing machine to ensure that the precursor could be in uniform contact with the graphite plate, then the graphite plate was loaded into a porcelain boat and placed in a tube furnace, nitrogen was pre-purged for 0.5 h at room temperature to remove air in the tube, the temperature was raised to 800 ℃ at a rate of 10 ℃ / min under a nitrogen atmosphere, and the sample was taken out after cooling to room temperature, thereby obtaining a low-dimensional coal-based hard carbon material. -1

[0060] The low-dimensional coal-based hard carbon material prepared above was used as a negative electrode of a sodium ion battery, and the sodium ion battery was assembled.

[0061] The prepared sodium ion battery negative material powder, Ketjen black and sodium carboxymethyl cellulose were mixed and ground according to a mass ratio of 8:1:1, the mixture was fully ground into fine powder, and then a proper amount of deionized water was added to continue grinding into a slurry with a suitable viscosity, the slurry was uniformly coated on a copper foil by using a coater, and then was dried in a vacuum at 110 ℃ for 10 h, and then was cut into a circular negative electrode sheet with a diameter of 10 mm by using a cutting machine for standby. The half battery was assembled in an argon-filled glove box, metal sodium was used as a counter electrode, and NaPF6 dissolved in dimethyl carbonate at a concentration of 1 mol was used as an electrolyte. A CR2025 type button cell was assembled, and then was allowed to stand for 8 h before electrochemical charge and discharge test. The test voltage range was 0.01 V-3 V, the current density was 0.02 Ag -1 , and the test results are shown in Figure 2 , the reversible specific capacity was 313.50 mAh g -1 , the initial coulombic efficiency was 90.37%, and the material had good electrochemical sodium storage performance.

[0062] Example 3

[0063] A synthesis method of a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, the material being prepared by crosslinking and deoxidation reduction of an oxidized coal nanosheet, an oxidized coal-based graphene quantum dot and p-phenylenediamine; specifically including the following steps:

[0064] ​The oxidized coal nanosheet and the oxidized coal-based graphene quantum dot (0.30 g of the oxidized coal nanosheet, the mass ratio of the oxidized coal nanosheet to the oxidized coal-based graphene quantum dot being 10:1) are dissolved in 30 mL of deionized water, 500 μL of a p-phenylenediamine solution is added after complete dissolution, and the mixture is stirred in a magnetic stirrer for 1 h, and then the uniformly mixed solution is poured into a 50 mL hydrothermal kettle, and the oxidized coal and the oxidized coal-based graphene quantum dot are allowed to fully crosslink with the p-phenylenediamine under the condition of 80℃ for 8 h. Finally, the crosslinked liquid is cold-dried to obtain a precursor.

[0065] The cold-dried precursor is clamped between two high-oriented pyrolytic graphite plates, and a 10 kPa pressure is applied to the graphite plates by an electric isostatic pressing machine to ensure that the precursor is in uniform contact with the graphite plates. Then the graphite plates are loaded into a porcelain boat and placed in a tube furnace, and the furnace is pre-purged with nitrogen for 0.5 h at room temperature to remove air in the tube; the temperature is raised to 1000℃ at a rate of 10℃ / min under a nitrogen atmosphere, and the sample is kept at 1000℃ for 6 h, and then taken out after cooling to room temperature, to obtain a low-dimensional coal-based hard carbon material. -1

[0066] The low-dimensional coal-based hard carbon material prepared above is used as a negative electrode of a sodium ion battery, and the sodium ion battery is assembled.

[0067] The prepared sodium ion battery negative material powder, Ketjen black and sodium carboxymethyl cellulose are mixed and ground according to a mass ratio of 8:1:1, and then ground into fine powder, and then a proper amount of deionized water is added to continue grinding into a slurry with a suitable viscosity, and the slurry is uniformly coated on a copper foil by a coater, and then dried in the shade, and then vacuum dried at 110℃ for 10 h, and then cut into a circular negative electrode sheet with a diameter of 10 mm by a cutting machine for standby. The half-cell is assembled in an argon-filled glove box, and metallic sodium is used as a counter electrode, and 1 mol of NaPF6 dissolved in dimethyl carbonate is used as an electrolyte. A CR2025 type button cell is assembled, and then left to stand for 8 h before electrochemical charge and discharge testing. The test voltage range is 0.01V-3V, and the current density is 0.02Ag -1 , and the test results are shown in Figure 3 , the reversible specific capacity is 342.5mAh g -1 , and the initial coulombic efficiency is 87.18%, and the material has good electrochemical sodium storage performance.

[0068] Example 4

[0069] A synthesis method of a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, the material being prepared by crosslinking and deoxidation reduction of an oxidized coal nanosheet and an oxidized coal-based graphene quantum dot with octanediamine; specifically including the following steps:

[0070] ​The oxidized coal nanosheet and the oxidized coal-based graphene quantum dot (0.30 g of the oxidized coal nanosheet, the mass ratio of the oxidized coal nanosheet to the oxidized coal-based graphene quantum dot being 30:1) are dissolved in 30 mL of deionized water, 600 μL of octanediamine solution is added after complete dissolution, and the mixture is stirred in a magnetic stirrer for 3 h, and then the uniformly mixed solution is poured into a 50 mL hydrothermal kettle, and the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot are crosslinked with octanediamine at 120 ℃ for 7 h. Finally, the crosslinked liquid is cold-dried to obtain a precursor.

[0071] The cold-dried precursor is clamped between two super-high-purity graphite plates, and a 10 kPa pressure is applied to the graphite plates by an electric isostatic pressing machine to ensure that the precursor is in uniform contact with the graphite plates. Then the graphite plates are loaded into a porcelain boat and placed in a tube furnace, pre-purged with nitrogen for 0.5 h at room temperature to remove air in the tube, and then heated to 1300 ℃ at a rate of 5 ℃ / min under a nitrogen atmosphere, and held for 3 h. After cooling to room temperature, the sample is taken out, and a low-dimensional coal-based hard carbon material is obtained. -1

[0072] The low-dimensional coal-based hard carbon material prepared above is used as a negative electrode of a sodium ion battery, and the sodium ion battery is assembled.

[0073] The prepared sodium ion battery negative material powder, Ketjen black, and sodium carboxymethyl cellulose are mixed and ground in a mass ratio of 8:1:1, and then ground into fine powder. An appropriate amount of deionized water is added and the slurry is ground into a slurry with appropriate viscosity. The slurry is uniformly coated on a copper foil with a coater, dried in the shade, and then vacuum dried at 110 ℃ for 10 h. The copper foil is cut into a circular negative electrode with a diameter of 10 mm using a cutting machine. The half-cell is assembled in an argon-filled glove box, and metal sodium is used as the counter electrode and 1 mol of NaPF6 dissolved in dimethyl carbonate is used as the electrolyte. A CR2025 type button cell is assembled, and after standing for 8 h, the electrochemical charge and discharge test is performed. The test voltage range is 0.01 V-3 V, and the current density is 0.02 Ag -1 . The test results are shown in Figure 4 , the reversible specific capacity is 371.24 mAh g -1 , and the initial coulombic efficiency is 92.26%, which has good electrochemical sodium storage performance.

[0074] Example 5

[0075] A synthesis method of a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, which is prepared by crosslinking and deoxidation reduction of oxidized coal nanosheets and oxidized coal-based graphene quantum dots with ethylenediamine; specifically comprising the following steps:

[0076] ​The oxidized coal nanosheets and oxidized coal-based graphene quantum dots (0.30 g of oxidized coal nanosheets, a mass ratio of oxidized coal nanosheets to oxidized coal-based graphene quantum dots of 30:1) were dissolved in 30 mL of deionized water, 300 μL of ethylenediamine solution was added after complete dissolution, and the mixture was stirred on a magnetic stirrer for 1 h, and then the uniformly mixed solution was poured into a 50 mL hydrothermal kettle, and the oxidized coal nanosheets and oxidized coal-based graphene quantum dots were allowed to fully crosslink with ethylenediamine under the condition of 100℃ for 5 h. Finally, the crosslinked liquid was cold-dried to obtain a precursor.

[0077] The cold-dried precursor was clamped between two super-high-purity graphite plates, and a 20 kPa pressure was applied to the graphite plates by an electric isostatic pressing machine to ensure that the precursor was in uniform contact with the graphite plates. Then the graphite plates were loaded into a porcelain boat and placed in a tube furnace, pre-purged with nitrogen for 0.5 h at room temperature to remove air in the tube, and then heated to 1300℃ at a rate of 5℃ / min under a nitrogen atmosphere, and held for 2 h. After cooling to room temperature, the sample was taken out, and a low-dimensional coal-based hard carbon material was obtained. -1

[0078] The low-dimensional coal-based hard carbon material prepared above was used as a negative electrode of a sodium ion battery, and the sodium ion battery was assembled.

[0079] The prepared sodium ion battery negative material powder, Ketjen black, and sodium carboxymethyl cellulose were mixed and ground in a mass ratio of 8:1:1, and then ground into fine powder. An appropriate amount of deionized water was added and the slurry was ground into a slurry with suitable viscosity. The slurry was uniformly coated on a copper foil using a coater, and then dried in a vacuum at 110℃ for 10 h. The copper foil was cut into a circular negative electrode with a diameter of 10 mm using a cutting machine. The half-cell was assembled in an argon-filled glove box, and metallic sodium was used as the counter electrode, and 1 mol of NaPF6 dissolved in dimethyl carbonate was used as the electrolyte. A CR2025 type button cell was assembled, and after standing for 8 h, the electrochemical charge and discharge test was performed. The test voltage range was 0.01V-3V, and the current density was 0.02Ag -1 . The test results are shown in Figure 5 , the reversible specific capacity was 348.4mAh g -1 , and the initial coulombic efficiency was 89.84%, showing good electrochemical sodium storage performance.

[0080] Example 6

[0081] A synthesis method of a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, the material being prepared by crosslinking and deoxidation reduction of oxidized coal nanosheets and oxidized coal-based graphene quantum dots with polyether amine; specifically comprising the following steps:

[0082] ​The oxidized coal nanosheet and oxidized coal-based graphene quantum dots (0.30 g of oxidized coal nanosheet, mass ratio of oxidized coal nanosheet to oxidized coal-based graphene quantum dots 20:1) were dissolved in 30 mL of deionized water, 300 μL of polyether amine solution was added after complete dissolution, and the mixture was stirred in a magnetic stirrer for 1 h, then the uniformly mixed solution was poured into a 50 mL hydrothermal kettle, and the oxidized coal nanosheet and oxidized coal-based graphene quantum dots were allowed to fully crosslink with the polyether amine under the condition of 100 ℃ for 6 h. Finally, the crosslinked liquid was cold-dried to obtain a precursor.

[0083] The cold-dried precursor was clamped between two super-high-purity graphite plates, and a 20 kPa pressure was applied to the graphite plates by an electric isostatic pressing machine to ensure uniform contact between the precursor and the graphite plates. Then the graphite plates were loaded into a porcelain boat and placed in a tube furnace, pre-purged with nitrogen for 0.5 h at room temperature to remove air in the tube, and then heated to 1300 ℃ at a rate of 5 ℃ / min under a nitrogen atmosphere, and held for 2 h. After cooling to room temperature, the sample was taken out, which was a low-dimensional coal-based hard carbon material. -1

[0084] The low-dimensional coal-based hard carbon material prepared above was used as the negative electrode of a sodium ion battery, and the sodium ion battery was assembled.

[0085] The prepared sodium ion battery negative material powder, Ketjen black and sodium carboxymethyl cellulose were mixed and ground in a mass ratio of 8:1:1, and then ground into fine powder. An appropriate amount of deionized water was added and the slurry was ground into a slurry with suitable viscosity. The slurry was uniformly coated on a copper foil with a coater, and then dried in a vacuum at 110 ℃ for 10 h. The copper foil was cut into a circular negative electrode with a diameter of 10 mm using a cutting machine. The half-cell was assembled in an argon-filled glove box, and metallic sodium was used as the counter electrode, and 1 mol of NaPF6 dissolved in dimethyl carbonate was used as the electrolyte. A CR2025 type button cell was assembled, and after standing for 8 h, the electrochemical charge and discharge test was carried out. The test voltage range was 0.01 V-3 V, and the current density was 0.02 Ag -1 , and the test results are shown in Figure 6 , the reversible specific capacity was 420.40 mAh g -1 , and the initial coulombic efficiency was 91.97%, which had good electrochemical sodium storage performance.

[0086] Example 7

[0087] A synthesis method of a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, which is prepared by crosslinking and deoxidation reduction of oxidized coal nanosheet and oxidized coal-based graphene quantum dots with polyimide; specifically comprising the following steps:

[0088] ​The oxidized coal nanosheet and the oxidized coal-based graphene quantum dot (0.30 g of the oxidized coal nanosheet, a mass ratio of the oxidized coal nanosheet to the oxidized coal-based graphene quantum dot being 30:1) are dissolved in 30 mL of deionized water, 400 μL of a polyimide solution is added after complete dissolution, and the mixture is stirred in a magnetic stirrer for 1 h, and then the uniformly mixed solution is poured into a 50 mL hydrothermal kettle, and the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot are allowed to fully crosslink with the polyimide under the condition of 100℃ for 6 h. Finally, the crosslinked liquid is cold-dried to obtain a precursor.

[0089] The cold-dried precursor is clamped between two super-high-purity graphite plates, and a 20 kPa pressure is applied to the graphite plates by using an electric isostatic pressing machine to ensure that the precursor can be in uniform contact with the graphite plates. Then the graphite plates are loaded into a porcelain boat and placed in a tube furnace, and the tube is pre-purged with nitrogen for 0.5 h at room temperature to remove air in the tube; the temperature is raised to 1300℃ at a rate of 5℃ / min under a nitrogen atmosphere, and the sample is kept at 1300℃ for 2 h, and then the sample is taken out after cooling to room temperature, and the low-dimensional coal-based hard carbon material is obtained. -1

[0090] The low-dimensional coal-based hard carbon material prepared above is used as a negative electrode of a sodium ion battery, and the sodium ion battery is assembled.

[0091] The prepared sodium ion battery negative material powder, Ketjen black and sodium carboxymethyl cellulose are mixed and ground according to a mass ratio of 8:1:1, and then the mixture is fully ground into fine powder, and then an appropriate amount of deionized water is added to continue grinding into a slurry with a suitable viscosity, and then the slurry is uniformly coated on a copper foil by using a coater, and then the copper foil is dried in a vacuum at 110℃ for 10 h, and then the copper foil is cut into a circular negative electrode sheet with a diameter of 10 mm by using a cutting machine for standby. The half battery is assembled in an argon-filled glove box, a metal sodium is used as a counter electrode, and 1 mol of NaPF6 dissolved in dimethyl carbonate is used as an electrolyte. A CR2025 type button cell is assembled, and then the button cell is allowed to stand for 8 h, and then the button cell is subjected to electrochemical charge and discharge test. The test voltage range is 0.01V-3V, the current density is 0.02Ag -1 , and the test results are shown in Figure 7 , the reversible specific capacity is 329.05 mAh g -1 , the initial coulombic efficiency is 97.59%, and the sodium ion battery has good electrochemical sodium storage performance.

[0092] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.​

Claims

1. A method for preparing a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency, characterized in that, The oxidized coal nanosheet and the oxidized coal-based graphene quantum dot are obtained by oxidizing and depolymerizing Xinjiang bituminous coal by using a liquid phase oxidation method; the mixture of the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot or the oxidized coal nanosheet is cross-linked, self-assembled and deoxidized and reduced by using an amine-containing compound, so as to obtain a low-dimensional coal-based precursor; the coal-based precursor is calcined by using a graphite plate as an auxiliary, the graphite plate is clamped in the middle of the coal-based precursor, and a fixed pressure is applied to the graphite plate; Then, the low-dimensional coal-based hard carbon material is prepared by high-temperature calcination. The amine-containing compound is any one of ethylenediamine, octanediamine, o-m / p-phenylenediamine, diethylenetriamine, triethylenetetramine, polyether amine, polyimide, piperazine or urea; after the amine-containing compound is added, the mixture is hydrothermally treated at 80-120 ℃ for 4-8 h; the mass-volume ratio of the oxidized coal nanosheet to the amine-containing compound is 3 g:1-8 mL.

2. The method for preparing a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency according to claim 1, characterized in that, The Xinjiang bituminous coal is oxidized and depolymerized by using a nitric acid / sulfuric acid oxidation system for 3-6 h, and the mass-volume ratio of the coal powder to the oxidation system is 1 g:24 mL; the volume ratio of sulfuric acid to nitric acid is 1:1-3:

1.

3. The method for preparing low-dimensional coal-based hard carbon material with both high sodium storage capacity and high initial coulombic efficiency according to claim 1, characterized in that, The mass ratio of the oxidized coal nanosheet to the oxidized coal-based graphene quantum dot is 3:1-100:

1.

4. The method for preparing the low-dimensional coal-based hard carbon material with both high sodium storage capacity and high initial coulombic efficiency according to claim 1, characterized in that, The graphite plate is any one of ordinary graphite, high-purity graphite, ultrahigh-purity graphite or highly oriented pyrolytic graphite, and the fixed pressure ranges from 3 kPa to 30 kPa.

5. The method of claim 1, wherein the low-dimensional coal-based hard carbon material having high sodium storage capacity and high initial coulombic efficiency is prepared by the steps of: (a) preparing a coal-based carbon material; (b) performing a first activation process on the coal-based carbon material; (c) performing a second activation process on the coal-based carbon material; and (d) performing a third activation process on the coal-based carbon material. The high-temperature calcination is heating to 800-1500 ℃ under the protection of nitrogen atmosphere, the holding time is 1-6 h, and the heating rate is 1-10 ℃ / min -1 .

6. The method of claim 1, wherein the low-dimensional coal-based hard carbon material having high sodium storage capacity and high initial coulombic efficiency is prepared by the steps of: (a) preparing a coal-based carbon material; (b) performing a first activation process on the coal-based carbon material; (c) performing a second activation process on the coal-based carbon material; and (d) performing a third activation process on the coal-based carbon material. The method comprises the following steps: (1) The Xinjiang bituminous coal is subjected to liquid phase oxidation in a nitric acid / sulfuric acid oxidation system, and the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot are obtained by centrifugation, dialysis, rotary evaporation and cold drying; (2) The mixture of the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot or the oxidized coal nanosheet is dissolved in deionized water, and the mass-volume ratio of the oxidized coal nanosheet to the deionized water is 1 g:100 mL; (3) After the two are completely dissolved in water, an amine-containing compound is added, and magnetic stirring is performed for 1-8 h; (4) The mixture is placed in a hydrothermal kettle for hydrothermal reaction, so that the amine-containing compound is fully cross-linked with the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot; (5) The cross-linked mixture is cold-dried to obtain a low-dimensional coal-based hard carbon precursor; (6) The graphite plate clamping the low-dimensional coal-based hard carbon precursor is loaded into a tube furnace, and is calcined at high temperature in an inert atmosphere to obtain a low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency.

7. The method for preparing a low-dimensional coal-based hard carbon material with both high sodium storage capacity and high initial coulombic efficiency according to claim 1 or 6, characterized in that, Preparation of the oxidized coal nanosheet and the oxidized coal-based graphene quantum dot: (a) The Xinjiang bituminous coal is ball milled to pass through a 200-mesh sieve to obtain coal powder; (b) 30 g of the coal powder is added into a container, and 720 mL of a mixed solution of sulfuric acid and nitric acid is slowly added under stirring for 3-6 h; (c) After the reaction is completed, the mixture is diluted into 3 L of deionized water, and is centrifuged at a speed of 8000-10000 rpm for 5-10 min; (d) After the upper acid solution is poured out, the precipitate in the centrifuge tube is dissolved in 3-5 L of deionized water, and is ultrasonically treated for 1-3 h to completely dissolve the precipitate, and then is loaded into a dialysis bag for dialysis; (e) After the solution is dialyzed to neutral, centrifugation is performed again, at this time, the large particles that are not completely oxidized are precipitated, and the supernatant is concentrated at 60-80 ℃ using a rotary evaporator; (f) Finally, the concentrated solution is freeze-dried, and the oxidized coal-based graphene quantum dots are obtained; the large particles precipitated are collected to obtain oxidized coal nanosheets.

8. The low-dimensional coal-based hard carbon material with high sodium storage capacity and high initial coulombic efficiency prepared by the method of any one of claims 1-7.

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